We review two recent advances in coupled quantum mechanics/molecular mechanics (QM/MM) modeling for metallic materials. The QM/MM methods are formulated based on quantum mechanical charge density embedding. In the first method, QM/MM coupling is accomplished by an embedding potential evaluated via orbital-free density functional theory. The charge density embedding in the second QM/MM method is achieved through constrained density functional theory. The extension of QM/MM coupling to the quasicontinuum method is illustrated, offering a route toward quantum mechanical simulations of materials at micron scales and beyond. The theoretical formulations of the QM/MM methods are discussed in detail. We also provide some examples where the QM/MM methods have been applied to understand fundamental physics in a wide range of material problems, ranging from void formation, pipe diffusion along dislocation core, nanoindentation of thin films, hydrogen-assisted cracking, magnetism-induced plasticity to stress-controlled catalysis in metals. An outlook to future development of QM/MM methods for metals is envisioned.

89.Duster, A., Wang, C.H., Garza, C., Miller, D., and Lin, H.: Adaptive QM/MM: Where are we, what have we learned, and where will we go from here?Wiley Interdiscip. Rev.: Comput. Mol. Sci.7, e1310 (2017).